Support for the research leading to this invention was sponsored, in part, by the National Institute of Health. This support is gratefully acknowledged by the inventors.
A basic problem in peptide synthesis is one of blocking or protecting the amino group from interaction with a carboxyl group on the same amino acid. These undesirable side reactions are prevented by attaching to one amino acid a group that will render the --NH.sub.2 group unreactive and still permit the desired reaction to take place. In addition to providing protection for the amino group, the blocking group is preferably one that can be easily removed without chemically altering the remainder of the molecule including the peptide linkage that has been built up during the synthesis. (See generally, Morrison and Boyd, Organic Chemistry, Third Ed., Sec. 30.10 Synthesis of Peptides, pp. 1131-1133 (1983).
Attempts to develop a two-support continuous solid phase technique for peptide synthesis (inverse Merrifield method) using a 9-Fluorenylmethyloxycarbonyl group (FMOC) for amino protection have been hindered due to incomplete scavenging of dibenzofulvene by the polymeric deblocking agents. These problems were partially overcome through use of the the 2-Chloro-1-indenylmethoxycarbonyl group (Climoc) for protection of amino groups (see U.S. Pat. Nos. 4,581,167 and 4,394,519 to Carpino, et al.). The present invention has devised a scheme for the development of new, Michael-addition based amino-protecting groups for which the deblocking and scavenging steps are one and the same.
The present invention is directed to compounds containing novel Michael addition based amino-protecting groups, such as 2-(t-butyl-sulfonyl)-2-propenyloxycarbonyl groups and the like. The use of the compounds of the present invention in peptide synthesis overcomes the problems resulting from ineffective scavenging occurring when the FMOC or Climoc groups are utilized as the protecting groups.
The 2-(t-Butylsulfonyl)-2-propenyloxycarbonyl group (Bspoc) and related Michael Addition-based amino-protecting groups described herein are superior for peptide synthesis. Deblocking is exceptionally rapid under mild, nonhydrolytic conditions, resulting in faster syntheses of long chain peptides with fewer side reactions, such as diketopiperazine, pyroglutamic acid and succinimide formation, thereby leading to higher yields and greater purity of the products. Due to the stability against acidic reagents, acid chlorides may be used as quick-acting coupling agents, further speeding up the process. Moreover, no significant racemization occurs in either the coupling or deblocking steps.